WESTPORT — The concentration of a potentially cancer-causing chemical in the Fall River water supply used by some Westport residents is less than the state allows, according to the state Department of Environmental Protection.

The DEP said the water supply tested at 52 parts per billion for trihalomethane, below the state limit of 80 parts per billion.

Still, DEP spokesman Jim Ferson said Westport was required to send out a notice to 158 customers, letting them know that the THM count is still high.

Ferson said the town must average out the last four quarters. He said last summer, the town had a level of more than 160 parts per billion.

Based on that high figure, the town's average is more than 90 parts per billion, according to Ferson.

Linda Correia, a Westport water authority, could not be reached for comment.

Both former Town Administrator John Healey and Selectmen Chairman Antone Vieira Jr. said this past spring that town officials were working hard to flush the water line and lower the levels. Both said this action would hopefully convince the state DEP not to force Westport to invest in a water treatment plant.

The town began flushing the line during the spring of 2013.

Trihalomethanes form when natural organic material, such as the decaying vegetation commonly found in lakes and reservoirs, reacts with chlorine used to treat the water, according to the EPA. They are considered possible carcinogens.